Dry pet foods for dogs and cats have been primarily prepared by extrusion. A heated food mass which is sufficiently plastic to be extruded using an ordinary screw extruder wherein expansion of the food occurs is worked in the extruder and emerges from the extruder usually in a strand or flat type rectangular sheet, depending upon the die shape, and is then cut and/or shaped into discrete particles. In this manner, dry diets utilizing kibbles, a particular discrete particle, are prepared. These kibbles should be dimensionally stable. That is, they retain the same shape as when immediately prepared and then packaged. They do not spontaneously crumble or lose fines to any great extent, even when subjected to mild pressure. Over time the physical and dimensional stability of the kibble is maintained.
This physical integrity of the extruded shape is at least partially dependent upon the chemical nature of the extruded material. When carbohydrate content is low, generally below about 19 wt % of the food composition, expansion of the food mass during the extrusion process is significantly reduced because of the reduced matrix formation generally obtained from the presence of carbohydrate such as a starch or grain. The relatively low carbohydrate, high protein, high fat food masses when extruded under normal conditions do not expand significantly, thereby providing a discrete particle which is not dimensionally stable. Additionally, the discrete particle can have difficulty retaining added fat, particularly when the fat is added to the outside of the particle, such as by spraying. Such extruded particle is not dimensionally stable and can not be packaged for appropriate commercial use.
It has now been discovered that a relatively low carbohydrate, relatively high protein and fat content pet food can be successfully extruded into a discrete particle, which is dimensionally stable. It has the physical attributes of typical commercial pet foods which include much higher levels of carbohydrate. Additionally where fat absorption can be a problem, the article matrix is able to absorb and retain fat.